Reliability of isokinetic tests of velocity- and contraction intensity-dependent plantar flexor mechanical properties.

'Flexibility' tests are traditionally performed voluntarily-relaxed by rotating a joint slowly, however functional activities are performed rapidly with voluntary/reflexive muscle activity. Here we describe the reliabilities and differences in maximum ankle range of motion (ROMmax ) and plantar flexor mechanical properties at several velocities and levels of voluntary force from a new test protocol on a commercially available dynamometer. Fifteen participants had their ankle joint dorsiflexed at 5, 30, and 60°. s-1 in two conditions: voluntarily-relaxed and whilst producing 40% and 60% of maximal eccentric torque. Commonly reported variables describing ROMmax and resistance to stretch were subsequently calculated from torque and angle data. Absolute (coefficient of variation (CV%) and typical error) and relative (ICC2,1 ) reliabilities were determined across two testing days (≥72 h). ROMmax relative reliability was good in voluntarily-relaxed tests at 30 and 60°. s-1 and moderate at 5°. s-1 , despite CVs≤10% for all velocities. Tests performed with voluntary muscle activity were only reliable when performed at 5°. s-1 , and ROMmax reliability was moderate and CV ≤8%. For most variables, the rank order of participants differed between the slow-velocity, relaxed test and those performed at faster speeds or with voluntary activation, indicating different information. A person's flexibility status during voluntarily relaxed fast or active stretches tended to differ from their status in the traditional voluntarily relaxed, slow-velocity test. Thus, 'flexibility' tests should be completed under conditions of different stretch velocity and levels of muscle force production, and clinicians and researchers should consider the slightly larger between-day variability from slow-velocity voluntarily-relaxed tests.